RADIO HABANA CUBA
DXERS UNLIMITED
MID-WEEK EDITION
TUESDAY, MAY 01, 2001
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hi amigos! Welcome to a very special edition of Dxers Unlimited, coming to you from Radio Havana Cuba, I am Arnie Coro and today our station is celebrating its 40th year on the air... Yes, today, MAY DAY 2001, we are celebrating our 40th birthday!
Actually, as many of you have heard in the past, we started test broadcasts earlier in 1961, under the name Onda Corta Experimental Cubana, or Cuban Experimental Short Wave, but during the Victory Parade of May Day 1961 when Cuba was celebrating the Victory over the invading mercenary forces of the CIA-organized Brigade 2506, that was when my dear colleagues Orlando Castellanos and Fernando Alcorta went on the air from Havana's Revolution Square, the Plaza de la Revolucion, using for the first time ever the name Radio Havana Cuba for the station.
And I remember that day very well, as I was the person in charge of installing the REL Built 161 megaHertz remote link from Revolution Square to our downtown studios, not an easy job, as the big corner reflector antenna was the only one available, and it was very difficult to install at the base of the "Jose Marti" Memorial. My mentor, senior engineer Carlos Estrada, was very pleased with the results, and from then on, for several years, every time we had a remote broadcast, he asked me to install the VHF link from the remote site to the studios.
There are many other interesting stories about our first years on the air, which someday I would like to share with you, too.... Today, I am happy as any person in this world can be seeing the station developing, upgrading its technology, going to digital audio, with an Internet presence and above all, with a group of young people who will surely replace all of us very well when we retire.
Now item two: Very quiet SOL... yes the SUN is now very quiet, and the BIG SPOT region 9433 is about to turn around again. During this Carrington rotation it did not generate X type flares, just an M7 X ray flare. More about the SUN and HF propagation conditions at the end of the show when I'll bring you Arnie Coro's HF plus 6 meters propagation update and forecast...
Item three: Summer Sporadic E season just starting up, so it's a good time to install a 10 meter band antenna to enjoy what's left of F2 propagation and the Summer Short Skip season, so today, at the request of many Dxers Unlimited's fans, I will provide detailed information on how to build your simple ASD or Asymmetric Dipole Antenna for the 10 meter band...
Stay right on this frequency, and keep paper and pen or pencil handy, as I will be repeating our listserver's instructions on how to subscribe to Dxers Unlimited's mailing list, now distributing our scripts and other information in HTML format... Margarita Delgado is my sound engineer and producer... I am Arnie Coro in Havana, celebrating today Radio Havana Cuba's 40th birthday, amigos! Stay tuned, I'll be back in a few seconds....
You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited and here is item two: Our very popular ANTENNA Section of the program... At the request of many listeners, here are the dimensions for the 10 meter band Asymmetric SLOPING DIPOLE in its most compact possible form. The antenna has two legs or branches, one is one quarter of a wavelength at the operating frequency, like in a standard HALF WAVE DIPOLE, but the other leg of this antenna is THREE QUARTERS wavelengths long... Hence the name ASYMMETRIC DIPOLE. You install this antenna sloping in the direction that you want to listen or to transmit, or both if you are an amateur radio operator already.
The antenna is fed with standard 50 ohm coaxial cable, you can use RG58U for short runs, of less than 30 meters or 100 feet, or use RG8 or RG213 for longer cable runs, or when you are using high power. Of course, you can use RG213 or RG8 even when your station is running low power, but the other way around it doesn't hold, that is, you MUST USE the half inch diameter cable for high power work ALWAYS.... Now, calculate the length of a half wave dipole by using the formula 143 divided by the frequency in Megahertz... this will give you the approximate length of a standard dipole, divide the results by two and you will have the length of a quarter of a wavelength at the operating frequency.
Once again, I MUST remind you that you will start up testing your antenna with this length, and that typically your antenna will require trimming its length due to the many surrounding objects that are close to your particular antenna, and which no formula can predict!!! Now, the length of the long leg of the asymmetric dipole is three times the length of the short leg.... That's easy to remember... This is the shortest possible ASD antenna, you can make a longer one with more directivity if you wish, just by making the long leg five or seven quarters of a wavelength long.
SO, let's do the numbers together: We are designing an ASD antenna for the lower segment of 10 meters between 28. and 28.5 megaHertz, to be able to work DX stations that operate there both on CW and SSB, and we will also be able to hear the beacon's band that spans from 28.2 to 28.3 MegaHertz. SO, divide 143 by 28.5 ... That equals 5.01 meters. Then we divide this result by two: and that equals 2.5 meters. So we build the antenna with the short leg of 2.5 meters and the long leg of 7.5 meters. The coaxial cable connects to the feedpoint with the shield or braid to the SHORT LEG, which must be installed to the top of the mast or supporting structure. The center conductor of the coaxial cable goes to the long leg of the antenna, which is the one that slopes down at an angle anywhere from 30 to 45 degrees... AND DO REMEMBER to make the wire slope in the DIRECTION YOU WANT TO WORK.
As you may realize, this is a very simple antenna to build yourself land install; it requires just one tall mast, and actually you can install two, three or even four of them using a single mast.... you then switch between antennas, and your coverage is no longer in just one direction. By judiciously selecting the azimuths in the direction your ASDs are sloping, you can work a lot of DX with these simple antennas. DO REMEMBER that you must trim the length of both legs carefully after installing the antenna to obtain the lowest possible Standing Wave Ratio or, if your antenna shows an SWR of 2 to 1 or less, just run it through an antenna tuner to your transceiver. Of course just for receiving, there is no need to go to such trouble -- the ballpark figures provided by the formula will work very well indeed for receive-only installations!
AS ALWAYS, if you have any doubts about the ASD for 10 meters, or any other radio hobby-related topic, please feel free to e-mail me with your questions... It is a great pleasure to answer them and as it happens on many occasions, to then have the opportunity of talking to you on the amateur bands... My e-mail address arnie@radiohc.org, and if you are not yet in cyberworld, just send a postcard with your radio hobby related questions to Arnie Coro, Radio Havana Cuba, Havana Cuba.
By the way you can hear my ASD 10 meter band antenna almost every day by monitoring 28.5 megaHertz plus or minus five kiloHertz, my usual operating range while enjoying the nice propagation conditions on the 10 meter amateur band! Now with even more chances for short skip contacts, as the wonderful 28 megaHertz amateur bands start to enjoy the summer sporadic E skip season...
You are listening to a very special 40th Anniversary Edition of Dxers Unlimited... Yes we are all here at the station celebrating 40 years of continuous broadcasts from Cuba. And now here is item three of today's program: Field effect transistors make wonderful regenerative detectors when they are working on a properly designed circuit. During a recent debate about FET regenerative detectors' performance, as compared with the classic vaccum tubes, a very experienced senior engineer said something that I will remember well forever. He said, "Arnie, a typical junction FET like the old reliables 2N3819 and MPF102 will make a wonderful regenerative detector stage when the circuit parameters are the appropriate ones. You can't just throw the Field Effect Transistor into a vacuum tube circuit diagram, reduce the voltage, and ask the thing to work properly." And he added, "YES, it will work, you will pick up stations, but it can be made to operate much better by using a circuit design especially made for the Field Effect Device."
By the way, this comment came after I showed my very experienced senior engineer friend the prototype of the SOLID STATE REGENERODYNE receiver, which he liked very much, to such an extent as to suggest that I should write an article about this radio and make it available at our Dxers Unlimited website, something I will be certainly doing during the next few weeks...
The SOLID STATE REGENERODYNE receiver could be an ideal project to be made into an easy to assemble low parts count radio receiver kit! So far, the results obtained on the two bands that I have the prototype operating are really excellent, providing very good sensitivity, and excellent selectivity, plus a nice audio quality too... The SOLID STATE REGENERODYNE prototype is operating now from 10 to 12 megaHertz, and that was the first band I tested, for a very logical reason -- I had the quartz crystal at hand for the local oscillator, now a second band was added, remember that the basic regenerative detector is working from 2 to 4 megaHertz, so the second band was achieved by using a crystal on a frequency of 12 megaHertz, making reception possible on the REGENERODYNE from 14 to 16 megaHertz, thus bringing in the 20 meters amateur band and the 19 meters international short wave broadcast band with excellent results, very good bandspread and what I consider also very important, a very nice calibration. NO, it is not a digital readout, but believe me, once I calibrated the 2 to 4 megaHertz basic tuning range, the readout on the analog dial is very reproduceable. So amigos, GOOD NEWS: Arnie Coro's SOLID STATE REGENERODYNE RECEIVER PROJECT is almost finished now, and soon to be made available at our website!!!!
And now, as always, at the end of the show, here is Arnie Coro's Dxers Unlimited propagation update and forecast: Summer Sporadic E season now in progress, watch for that nice short skip, and low band channels TV DX.... Solar flux hovering around 185 and holding steady... possibly declining during the next few days... The ionosphere is now receiving much more thermal energy from the Sun, so we will see the typical summer expansion that lowers the daytime maximum useable frequencies quite a bit... The effective sunspot number was 145 on Tuesday, and I expect it to go down a bit on Wednesday.
Best nighttime reception for short wave listening will be available from 9 to 16 megaHertz, while daytime DX signals via the F2 layer will be coming in from 14 to 22 megaHertz, with possible short periods of 10 meter band, that is 28 megaHertz openings... See you on 10 meters if it opens up amigos!!! Listen on 28.500 plus or minus 5 kiloHertz for CO2KK, and if you are already an amateur radio operator, let's have a nice QSO!
Arnie Coro CO2KK
Havana, Cuba
May 1, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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